Electron transfer reactions are crucial steps in a wide variety of biological transformations ranging from photosynthesis or aerobic respiration. Studies of electron transfer reactions in both chemical and biological systems have led to the development of a large body of knowledge and a strong theoretical base, which describes the rate of electron transfer in terms of a small number of parameters.
Electronic tunneling in proteins and other biological molecules occurs in reactions where the electronic interaction of the redox centers is relatively weak. Semiclassical theory reaction predicts that the reaction rate for electron transfer depends on the driving force (−ΔG°), a nuclear reorganization parameter (A), and the electronic-coupling strength between the reactants and products at the transition state (HAB), according to the following equation:kET=(4π3/h2λkBT)1/2(HAB)2exp [(−ΔG°+λ)2/λkBT]
The nuclear reorganization energy, λ, in the equation above is defined as the energy of the reactants at the equilibrium nuclear configuration of the products. For electron transfer reactions in polar solvents, the dominant contribution to λ arises from the reorientation of solvent molecules in response to the change in charge distribution of the reactants. The second component of λ comes from the changes in bond lengths and angles due to changes in the oxidation state of the donors and acceptors.
Previous work describes using change in reorganization energy, λ, as the basis of novel sensor. See for example, U.S. Pat. Nos. 6,013,459, 6,013,170, 6,248,229, and 7,267,939, all herein incorporated by reference in their entirety. The methods generally comprise binding an analyte to or near a redox active complex. The redox active complex comprises at least one solvent accessible redox active molecule and a capture ligand which will bind the target analyte, and the complex is bound to an electrode. Upon analyte binding, the reorganization energy of the redox active molecule decreases to form a solvent inhibited redox active molecule, to allow electron transfer between the solvent inhibited redox active molecule and the electrode.
It is an object of the present invention to provide composition and methods for the detection of target analytes using alteration in the solvent reorganization energy, corresponding to changes in the E0 of redox active molecules.